It is now widespread practice to construct various kinds of buildings, but especially commercial and industrial buildings, by on site erection and assembly of structural concrete panels which are either precast on site and tilted into position, or precast elsewhere and brought to the site. In the latter case, the panels are normally cast flat, lifted to the vertical, and then transported while substantially vertical and lifted into position on site.
It is of course imperative in the handling of these large structural panels as they are tilted, transported and moved into position that there be no risk whatever that they will fall. An established system for handling the panels involves an anchor cast in the panel and a clutch assembly by which a crane sling may be secured to the anchor. The anchor normally includes a head within the concrete body and an end which remains below the face or edge of the panel but is exposed within a recess. The clutch engages the anchor within this recess and is arranged so that the clutch cannot disengage while the panel is in a partially or wholly tilted orientation. One such arrangement is disclosed in U.S. Pat. No. 3,883,170 and is the basis of the commercial Frimeda system. Another approach is described in Australian patent 544832.
While these systems with an embedded anchor and safety clutch assembly have proven satisfactory in practice, they do have a significant disadvantage in that the steel anchors remain embedded in the panel in the erected building. In time, even though the original recess is capped or filled with mortar, the embedded steel anchor is a source of corrosion and can lead to discolouring in walls formed from the panels. There is also the economic issue that a relatively heavy steel component is essentially only used once and is in effect discarded because it cannot be practically recovered for reuse.
Any improved panel handling system should preferably be adaptable to both facelift and edgelift systems.
There have been at least two attempts to address these issues by providing a substantially plastic component in the panel. Australian patent 488954 proposes an arrangement in which the anchor component comprises a steel nut contained in an undercut enlargement at the end of a plastic tube cast in situ, and a threaded eyebolt is projected down the tube and attached to the nut for lifting. The steel component is much smaller, but this system has the significant disadvantage of the time required to screw and unscrew the eyebolt. In a somewhat similar approach described in Australian patent application 89982/91, a flat steel rectangular block is provided in an undercut enlargement in a rectangular plastic tube, and a pair of clutch shafts are inserted into the hole deformed by the tube. The shafts have end lugs which engage under the block and the system is locked by pushing in a secondary pin between the shafts to forcibly separate them. This system has been viewed as unsafe for transporting heavy building elements because of the risk of operator error in failing to insert the locking pin.
German patent application 195 23 476 discloses an arrangement in which an anchor body is rotatable to bring a pair of lugs beneath undercuts in a lined cavity, and then locked against return rotation by turning down a notched flap to engage the crane lift bar. Longitudinal voids are provided in the concrete for the passage of the crosshead extensions and lugs during insertion. These voids remain empty during lifting operations, and are a potential source of weakness as they could allow concrete to break away and flow into them. The rotatable load bearing element is a tube, and there is a cross-head spaced from the inner end of the cavity. This system requires, on attachment, four separate manual operations, ie. insertion, rotation, locking and crane hook engagement, and, on detachment, each of these four steps in reverse. Remote release is not an available option.